The present invention generally relates to vehicle brake systems and more particularly relates to a brake force booster with a panic braking function for automotive vehicles.
A brake force booster of this general type is disclosed in U.S. Pat. No. 5,645,145. During actuation, the valve piston of the prior art brake force booster interacts with a hydraulic piston which defines a first hydraulic chamber along with a force output member or a push rod. On the side of the hydraulic piston remote from the first chamber, there is a second hydraulic chamber which is connected to the first chamber by way of a plurality of channels, and the connection is closable by means of a valve assembly. A second hydraulic piston or annular piston is axially supported on the hydraulic piston, under the preload of a compression spring, the said piston permitting displacement of the fluid volume from the second chamber into the first chamber. Consequently, the described arrangement represents a hydraulic reaction device. The above-mentioned valve assembly is preferably configured so that it remains closed during xe2x80x98normalxe2x80x99 operation so that a transmission of the actuating force introduced at the valve piston and of the boosting force raised by the brake force booster occurs by means of the fluid volume enclosed in the first chamber. When a rapid actuation takes place, which is e.g. due to panic braking or emergency braking, the valve assembly remains open so that the fluid is displaced from the first chamber into the second chamber and the valve piston that is supported on the first hydraulic piston can cover a longer actuating travel, which causes an increase of the slot between the second sealing seat and a valve member and, thus, a quicker ventilation of the ventilatable working chamber of the prior art brake force booster.
The state of the art brake force booster especially suffers from the disadvantage of the complicated design of the mentioned means or the reaction device, whose chambers must be sealed by means of sealing elements which cause an increase of the friction developing in the system and, further, represent a potential source of disturbance. Further problems are involved with filling the hydraulic chamber with liquid pressure fluid, which is in particular inappropriate for large-scale production.
An object of the present invention is to disclose provisions which increase the reliability in operation and extend the useful life of the brake force booster. Another objective is to permit manufacture of the brake force booster disclosed by reasonable efforts.
According to the present invention, this object is achieved because the first sealing seat is arranged movably in relation to the control housing, and there is provision of a means by which the sealing seat can be fixed in position when a predetermined relative displacement between the valve piston and the control housing is exceeded so that the means permits a movement of the sealing seat in opposition to the actuating direction relative to the control housing. Consequently, decrease of the slot at the second sealing seat, the so-called poppet valve, which could be caused by movement of the sealing seat in the actuating direction is prevented.
To specify the idea of the present invention, it is provided that the first sealing seat is supported indirectly or directly on a reaction disc when the predetermined relative displacement between the valve piston and the control housing is exceeded. Thus, in the actuated condition, the deformation of the reaction disc causes the sealing seat to lift from its stop that is active in the actuating direction, and namely in opposition to the forces of a resetting spring.
In a preferred aspect of the present invention, a sleeve is associated with the valve piston in a way axially displaceable in relation thereto, the said sleeve including a stop as mentioned above, and the sealing seat, due to abutment on the stop, is supported on the reaction disc by means of the sleeve.